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A-1 Mechanical Blog

4 Sounds Your Furnace Shouldn’t Make


If you own a furnace, you’re undoubtedly familiar with the sound of its everyday operation. You know the noise it makes when it powers on, the sound of air whooshing through the vents, and the end of the heating cycle as it powers off. 

In fact, you’re so familiar with how it sounds that any out-of-the-ordinary noises come across as quite unusual and startling. Some common questions we get from homeowners about weird furnace noises include, “Why does my furnace make a loud noise when it turns off?” and “Why is my furnace clicking repeatedly?”

Let’s go over 4 unusual sounds furnaces make when they’re struggling to perform and inevitably need to be repaired. 

1. Loud Noise When It Powers Off

The furnace shut-down process should be fairly quiet. So hearing a loud noise as it powers down is concerning. The most common cause of a lot of noise after a furnace turns off is the sound of the ductwork contracting and expanding. 

Your home’s ductwork is composed of thin sheets of metal. They naturally get hot when the hot air produced by your furnace passes through the ductwork, and then cools down. As this happens, they contract and expand, making a loud noise once the heating cycle is finished. 

2. Repeated Clicking Noise at Startup

It’s normal to hear clicking noises as your furnace powers on. However, it’s unusual for the clicking noise to continue. If you have a gas furnace, a repeated clicking noise usually occurs because the gas burners are failing to ignite immediately. This should be checked out ASAP since it’s a safety concern.

3. Metal on Metal Noises

Your furnace is made up of a lot of moving metal parts. Sometimes they can come loose or detached and rattle around or bang against other metal parts. The result is the sound of metal hitting metal.

Sometimes the noise can sound like metal grinding against metal, resulting in a screeching or shrieking noise. This is especially common in furnaces that haven’t received annual maintenance. During a tune-up, our technicians lubricate the metal parts of your furnace to make sure they’re working properly.

4. The Furnace Booms When It Powers On

A booming sound is an alarming noise in a gas furnace because it sounds like a mini explosion. That’s because technically it is a mini-explosion. A booming sound results when there’s a delay in the ignition process. This could be due to any number of causes such as dirty or misaligned burners or a defective igniter. One thing is for certain: you don’t want the mini-explosion to become even bigger. Give us a call for a prompt repair.

The Bottom Line

Unusual furnace noises are your furnace’s way of telling you it needs some help. It’s essential to have a furnace you can depend on during the cold winter months. That’s why you should call us at the first “sound” of trouble. We’ll restore your furnace’s quiet operation.

Contact A-1 Mechanical Heating & Cooling for furnace repair in Lansing, MI. Comfort and Character You Can Depend On.

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